This invention relates generally to integrated gasification combined-cycle (IGCC) power generation systems, and more specifically to methods and systems for integrated water treatment of IGCC process water.
At least some known IGCC power plants generate large amounts of waste water and therefore require large amounts of make-up water. Siting versatility dictates using as little make-up water as possible and government regulations tend to require less waste water discharge off site. Initially designing a plant for zero wastewater discharge garners community acceptance and streamlines the permitting process. Recycling wastewater greatly decreases the amount of makeup water that must be purchased from the local utility and eliminates the local control and costs of sewer disposal. Wastewater recycling also allows a greater freedom in selecting a site for an industrial plant because there are fewer concerns about adequate water supply. In many cases, poor quality water can be used for make-up since it is upgraded in-house. For example, at several zero discharge sites, secondary sewage effluent or wastewater from other industrial sites is used as make-up.
Clean water laws such as the National Pollution Discharge Elimination System (NPDES) and the implementation of similar “zero liquid discharge” regulations at the local level are spurring treating highly saturated brine wastewaters such as cooling tower blowdown, which had previously been dumped into rivers. These wastewaters, saturated with calcium sulfate and silica, are difficult to evaporate because they are already at the scaling point. Current zero discharge waste water treating systems use a vapor recompression system, a forced circulation evaporator, and a spray dryer in series to treat process waste water. Frequent vaporizer system cleaning is required due to calcium and silica scaling. In addition the system has a high capital cost and power consumption since the chloride content in the gasification water system water is limited to 3500 parts per million (ppm). Higher chloride content in the gasification water system causes low pH values and corrosion since chloride recycled to the gasifier produces hydrochloric (HCl) acid.
Purified ammonium chloride recovered from wastewater can be sold as a byproduct to the fertilizer industry. The ammonium component is soluble and promotes plant growth. The chloride component is also soluble and provides soil chemistry balancing for low chloride soils.